ReRAM Startup Bets on Silver

LONDON — A resistive RAM non-volatile memory technology that could be embedded in SoCs and used in multilayered terabyte memory ICs is being brought to market by a well-backed and well-connected startup called Crossbar Inc.

The company, based in Santa Clara, California, has a working array that it claims validates its silver-ion based technology as a replacement for traditional non-volatile memory. This working chip is a CMOS access controller monolithically integrated with a memory array.

George Minassian, CEO of Crossbar, told EE Times that his company's embedded ReRAM technology will be available in 2014 and could be in the field in products such as microcontrollers in 2015. High-density monolithic memories based on the technology would then follow within a few quarters, he predicted.

Crossbar's memory technology is one of a number of alternative ReRAM offerings being researched by the industry. Most of these are trying to achieve equivalent or superior performance to NAND flash memory while being able to scale beyond the perceived two-dimensional limit for NAND flash at about 15 nanometers.

The resistence-switching mechanism within Crossbar's memory is based on the formation of a filament by the movement of silver ions from the top electrode within amorphous silicon. Source: Crossbar Inc.

Crossbar, founded in 2010, was formed to commercialize a body of memory device research based on metal-ion migration and filament formation within amorphous silicon that was being led by Professor Wei Lu at the University of Michigan. Professor Lu co-founded Crossbar and serves the company as chief technology officer. However, his amorphous silicon cross-point memory research was being nurtured by venture capital company Kleiner Perkins Caufield & Byers (KPCB) for a couple years prior to Crossbar's formation, according to Minassian.

The company has received $25 million in Series A and B rounds of funding and is backed by venture capital firms Artiman Ventures, KPCB, and Northern Light. Minassian told EE Times that Crossbar plans to demonstrate its memory array prototype at the upcoming Flash Memory Summit Aug. 13 to 15 as a signal that it is ready to begin product development.

Silver too expensive?Not really, when you get down to sub 20nm lithographic dimensions it is more about number of atoms used than the number of ingots. The possible problems with silver are more technical than they are fiscal. Although from a fabrication point of view not much more difficult than introducing copper, now routine.

Those who wish to pursue this silver based memory must first have a firm belief than NAND/NOR will not be able to evolve enough to do the job required of it in the future. The private sector does then give them the opportunity to help underwrite a possible winner. In analogy, the secret of success for those who wish to invest time and/or effort is to separate the signal from the noise.

Against all the potential problems that must be solved the Crossbar memory does appear to offer what I would call a win-win-win situation as an integral part of the memory cell in that it provides: uni-directional matrix isolation, allows the bidirectional current flow required for memory operation and reduces fabrication processing steps.

As somebody who in the past has looked at long carrier lifetime diodes to obtain reverse pulse current flow as well as punch through diodes for matrix isolation to me the Crossbar memory looks worth a development opportunity.

I think this is still a CBRAM, similar to the one used by Adesto. It relies on diffusing Ag. However, Adesto uses a chalcogenide rather than amorphous silicon. Amorphous silicon is highly temperature sensitive as it is still semiconducting silicon.

Having seen all too many claims about NAND/DRAM replacements over the past 20 years that will be ready for commercialization either next year or the next 2 years or the next 3 years, I have to express amazement that people still get tens of millions of dollars for this. Stan Ovshinsky was the ultimate expert at getting all sorts of companies from Intel to Exxon to give him literally hundreds of millions of dollars over decades for multiple wild projects, very few of which ever resulted any products and even fewer resulted in earnings of any sort. I think ENER might have been that last one and they too went bankrupt.

When someone talks about the magic of the private sector, I either laugh or grimace, depending on my mood at the time.